When I plugged in my external hard drive that was on Windows to a Linux machine (Raspberry Pi 3), it was automatically mounted at /media/brian/Brian-HD, but the permissions were drw- --- --- 1 brian brian. I needed Plex to be able to see and use the hard drive, but no matter how much I tried to open up permissions, the ls -l command never changed.

What worked for me

PLEX support forums has an article specifically on how to mount NTFS hard drives (but exFAT works too) so you can get permissions for PLEX to see the files. But their article is old and has broken links, so I will restate it with updated links:

Notices

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Disclosure: Some posts have references to Amazon products and I work at Amazon. I do not believe I have bias but this disclosure is to let you decide.